Color cinematography.



P. D. BREWSTER.

COLOR CINEMATOGRAPHY.

APPLICATION FILED Nov. 7. 1914.

1,258,136. Patented Jan. 8,1918.

WMM/Ime o: l 5 nv@ WISO/L $513714; SMOM/:QW LaMM FWL' PERCY D. BREVI STER, OF EAST ORANGE, NEW JERSEY.

COLOR CINEMATOGRAPHY.

Specification of Letters Patent.

Application filed November 7, 1914. Serial No. 870,753.

To all whom t may concern:

Be it known that I, PERCY I). BRnws'rEn, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements inColor Cinematography, of which the following is a full, clear, and exact description.

This invention relates to color photography particularly'color cinematography, of the class in which two optical images of the same object are projected on to two superposed sensitized surfaces in light of two different colors or groups of colors, so that upon development and further treatment two substantially complementary negative images are produced suitable for the printing of positives. Such a system is described in my copending applications Ser. Nos. 815,153, iiled January 29th, 1914,

841,797, filed May 29th, 1914 and 870,752,

filed Nov. 7, 1914, to'which reference may be made for a more complete explanation of the same; but it is to be understood that the procedure specically described in the applications is not the only one in which the invention can be advantageously employed.

The present invention has to do with the production of the negatives especially for cinematographic work, and its chief object is to provide a simple and effective method by which cinematographic film, coated on one side only and suitably sensitized can be utilized for the purpose. To this and other ends the invention consists in .the novel method and the novel steps thereof, hereinafter described.

In the accompanying drawing I have illustrated, somewhat diagrammatically, convenient and eective apparatus suitable for use in practising the invention, and referring now thereto,

Figure 1 is a sectional plan view of a camera for projecting the images on to the two superposed lms, Fig-1s. 2 and 3 are plan and side views, respectively, of the li ght-splitting prism employed in the camera. Fig. 4 is a detail side view of suitable intermittent film-feeding `mechanism. Figs.

of the base 1 with a front wall 2, in which is mounted the lens 3. Rays of light from the object (not shown) are projected by the lens 3 into the prism 4 against its surface 4a, provided with silvered bands 23, Fig. 3, 1n alternation with unsilvered or clear bands 24. The prism is banded with alternate Patented Jan. 8, 1918.

layers of silver, cemented on the clear spaces by Canada balsam to the prism G, so that part of the light projected by the lens is reflected by the silvered bands 23 into the prism 5 against the silvered surface 20 and thence onto the sensitized surface 8 in the film-gate 1U, while the other portions of the light are transmitted through the clear spaces 24 and prism 6 into prism 7, whence it is reected by the silvered surface of the prism 7 against the other sensitized surface, 9, in the film-gate. The images on the two sensitized surfaces by preference substantially congruent, but one image may be slightly larger than vthe other though in exact registry in the center of the picture. To produce congruence it is evident that the number of reflections in the case of' one image (either one) must be even and the other odd, such as one and two or two and three.

If the films 8, 9 aresensitized panchromatically it is necessary to interpose light filters 11, 12, in the paths of. the rays beyond or back of the prism 4, so that the image projected on one sensitized surface will be in light of one group of colors, say yellow-green to violet in the spectrum and on the other sensitized surface in light of another group of colors, say, red to yellowgreen, the two filters being in each case adapted toprevent the passage of light of the undesired color or colors. If one of the surfaces be sensitized chiefly for one colorA group in the spectrum, say, from yellowgreen to violet and the other surface chiey `for another colorfgroup, say from red to o their sensitized surfaces on the outside as shown in Fig. 5; o r the sensitized surfaces may be onfeither the outside or inside with a strip 26 of opaque material such as paper between the two films as illustrated in Fig. 6, to prevent light passing through one film lfrom acting` on the other and also to prevent the emulsions, under adverse weather conditions, from sticking together.

A. standard film feeding mechanism is illustrated diagrammatically vin Fig. 4, in which the claws 29 are adapted to pass through the usual perforations or sprocket holes in the two films and feed them both simultaneously. shown in Fig. 6, be used, itis to be under stoodthat any type of feeding mechanism, such as the Geneva or the dog movement, may be used to feed the separator and the two films together. The claws-29, containing the -slot 30 which is adapted to swing and slide on the stationary pin 31, is mounted to oscillate on the crank pin 34 attached to thef crank disk 32 which revolves on its center 33 in harmony with the shutter and the take-up and hlm-feeding mechanisms adapted to control the passage of the film through the camera, in the usual way. i

A camera employing two lenses is shown in Fig. 7, in which the two lenses 3 4 and 35, (adapted to form images of equal or almost equal size on the film) are protected by filters 36 and 37 respectively, the image projected by one lens being totally refiected twice by prism 38, one on its first reflecting surface at an angle of approximately 30 degrees'to the optical axis and the second time on the silvered surfaces 39 and thence onto the sensitized surface 26 of one of the films, while the light projected from lens 35 passes through block 40 and prism 41 and is refiected by the surface 42 against the sensitizedsurface 27 ,of the other film.

After the negative films are developed and fixed they lare laced on opposite sides of a double coated) positive film and the images printed fromv the negative film onto the two ,sides 0f the positive film as de- If the paper separator,

scribed in my application Ser. No. 841,797,

'afbove mentioned. Tn cinematographic work it is absolutely essential that these positive images be ,in proper registry, as the tiny pictures are in projection upon the screen enlarged to upward of a hundred and fortyfour diameters, or seventeen hundred times. if two entirely separate films be used (asin the drawing) should be of exactly the same width and fit very closely to the sides of the film gate and that they should be perforated simultaneously when their edges are absolutely even and-be fed through the film gate with the same claws.

The great advantage of feeding films, perforated simultaneously, throughv the same film gate, where they are exposed torabsolutely registering images, by means of the same claws, over the use of separate film it is preferable that they gates without means of determining whether the imagesfare exactly equal distances from the sides of the film'and from the perfora-v tions thereof, and the necessity of feeding Vthe film by means of two claws, is readily apparent, particularly lin view of the fact that a five hundredth bf an inch error in registration results in an error of from a quarter to three-eighths of an inch on the.

screen, thereby forming two separate images in different colors.

Inv the moving-picture projectors commonly used the light from the arc or other source is received by the condensing lens or lenses and is projected in the form of a cone of rays the apex of which is usually at the projecting lens. This cone of rays passes through the film, which ofcourse is between the projecting lens andthe condensers. It is therefore clear that although the axial ray is perpendicular t0 the film, the other rays are not. This means that if a given ray (other than the axial) strikes the rear surface of the film at a distance X from the mar 'n of the film it will not emerge from the ront surface at the same distance from the margin but at a distance X-t-D, in which expression the quantity D is quite small but nevertheless appreciable, depending, in general, upon the thickness of the film as well as upon the degree of taper of the cone of rays. Suppose, now, that the image on the rear surface andthe image on the front surface are exactly`superposed, one on the other, so that a ray perpendicular to one surface at a given point in the image thereon will pass perpendicularly through the corresponding point of the image on the other surface. Then it will be clear that if the ray is not perpendicular to the rear surface it will not pass through the corresponding point of the image on the front surface but will pass through some other point, nearer the center of the film. In other words, the two images will not be in perfect registry on the screen although they were perfectly superposed on the film. Moreover, since the rays at the margins of the cone are more inclined from the optical axis than are'the rays near the axis, 'the difference at the margins of the film will be greater than at points near the center. I therefore prefer to have the images in exact superposition only at the center, and have the rear-image (the one next tothe base of the cone of rays) sufficiently larger to compensate for the angularity of the non-axial rays. Then a ray which is inclined to the film will find in its path through the front surface a point of the front image corresponding exactly with the point through which it passed in the rear surface, and accordin ly the two images will register exactly ont e screen. Ifthe positives are made by contact printing, the images on one negative should be larger than those on the other, so that the images on one side of the positive film may be correspondingly larger than those on the other side. Such negatives can be made with the two lenscamera, shown in F ig. 7, by having one lens of longer focal length than the other so' as to produce a larger image on the film. Vith the one-lens camera, Fig. l, the lens may be corrected to bringI the redorange-yellow rays to a focus slightly farther from the lens than the other rays, so that the image formed on the red side will be correspondingly larger than that formed on the green side. Or the rays of one group can be made to pass through more glass than the others pass'through, as for instance one of the reflecting prisms may be larger than the corresponding prism on the other side. Then of course, the rays passing through the greater thickness of glass will come to afocus farther from the.

lens and will therefore give a correspondinglyvlarger image.

It is to be understood that this camera may be used for exposing the film described in my co-pending patent applications Ser. No. 814,797, before mentioned,-and`Ser. No. 846,966, filed June 24, 1914, in which the two films are vattached, temporarily or permanently, along one edge, the only modification necessary in the camera being to widen the film gate to permit of the passage of the wider film. This type of film is preferably perforated simultaneously through both films and the spacer (if used), and is fed through the film gate by the claws passing through the registering perforations in both films and acting simultaneously on them. i

In the appended claims I have used the expression registry-7 or suitable registry and the like, to mean such registry or superposition ,of the negative images as will permit the printing of positive images capable of projection upon a screen without material or appreciable separation of the images thereon.

I claim:-

l. In the art of color cinematography, the` steps comprising supporting in the same film gate two superposed sensitized lms, receiving light from a colored object and pro- -jecting the same, part with an odd number of reflections to one side of the superposed films and part with an even number of reflections to the other side, to produce two separate images in suitable registry, an image on each film, and developing both films to produce negative color-records of the object photographed.

2. In the art of two color cinematography, the method for producing negatives as herein described, comprising projecting from .the same point of view in different colors from opposite sides onto the sensitized surfaces of two films mounted face to face in the same film gate, two separate images in suitable registry, with an odd number of refiections of the light on one side of the films andan even number of reflections on the A other, and developing and fixing the films to obtain separate negative color-records of the object photographed.

3. In the art of color cinematography, the method herein described for producing negatives, comprising projecting from the same point of view separate re, 2;isteriny images in different colors or groups ofi/co ors from opposite s1des upon, color-sensitized surfacesA of two films\mounted in the same film gate and having feed-perforations in exact register by means of which thvsaid films are fed through the film gate, with an odd number of reflections of the light on one side of the films yand an even number of reflections on` the other, and developing and xing the said ries of perforations in exact register with each -otherfemploying such perforations for feeding the'two films simultaneously through the said film gate, and developing and fixing the two films.

5. In the art of color cinematography, the

method herein described for producing negaside of the films Asind an even number of retives, comprising projecting an image upon flections on the other, and developing and a film sensitized for one group of colors of 'fixing the two films. the spectrum and mounted lin a lm gate, In testimony whereof Iax my signature 5 and projecting from the opposite side a suitin' the presence of tWo subscribing' Witnesses. 15

ably registerin image ofthe same object on another lm sesitized for another group of BERCY BREWSTER' colors, -superposed on the rst Elm and Witnesses:

y mounted in the same film gate, with an odd M. LAWSON DYER,

1'0 number of reflections 'of the light on one S. S. DUNHAM. 

